For autonomous driving systems and driver-assistance systems to safely pilot vehicles, the systems may need to be able to determine the current state of road conditions with a high degree of accuracy, including conditions that were initially intended for use by a human. For example, throughout the world, the color that a traffic light is illuminated is used to determine whether a vehicle is permitted to proceed into an intersection or is required to stop before entering the intersection. An autonomous driving system or driver-assistance system controlling the vehicle may need to determine the state of a traffic light in order to safely control the vehicle in the vicinity of the intersection.